Multiscale Molecular Simulation Strategies for Understanding the Delignification Mechanism of Biomass in Cyrene

Abstract

In recent years, the cellulose-derived solvent Cyrene has piqued considerable interest in the green chemistry community despite only recently being available in the quantities required for solvent applications. Deconstruction of cellulose is an essential step in the production of fuel and value-added chemicals from lignocellulosic biomass. However, the high recalcitrance and heterogeneity of lignin hinder this process, necessitating the need to solubilize lignin. To understand the dissolution of lignin in Cyrene and Cyrene−cosolvent systems, multiscale molecular simulation approaches have been employed. Initially, the conductor-like screening model for real solvent (COSMO-RS) model was used to assess the thermodynamic properties of lignin in Cyrene and Cyrene−cosolvent systems. From the COSMO-RS calculations, the correlation between the predicted activity coefficient and the experimental lignin solubility was excellent. Further, classical molecular dynamics (MD) simulations were performed to evaluate the delignification of biomass by predicting structural and dynamic properties of lignin−solvent systems. The microscopic properties such as interaction energies, radius of gyration, solvent-accessible surface area, radial and spatial distribution functions (RDFs/ SDFs), and hydrogen bonds were assessed to characterize lignin dissolution in these solvent mixtures and were validated with experimental data. From the MD simulations, it was observed that lignin adopts a coil-like structure in Cyrene and Cyrene:water mixtures, thereby dissolving the lignin, while lignin adopts a collapsed-like structure in the presence of water. The occupancy density of Cyrene is highly surrounded by the aryl and hydroxyl groups of lignin polymer rather than by water. The interaction energies between lignin and Cyrene and Cyrene−cosolvent were much stronger than that between lignin and water, explaining the higher biomass delignification in Cyrene-based solvents.

Multiscale molecular simulations for the solvation of lignin in ionic liquids

“…By performing the quantum chemical calculations, the most stable conformer of lignin structure was obtained and used in the COSMO-RS calculations. The same chemical structure and stable conformer was used in our previous COSMO-RS calculations for lignin in amines, Cyrene, and protic ILs, and the results are in good agreement with experimental lignin solubility 8 , 63 , 64 .…”

Heuristic Computational Model for Predicting Lignin Solubility in Tailored Organic Solvents

“…In this work, we analyzed structure–solubility relationships between lignin pentamers and organic solvents across a large space of possible lignin/solvent compositions. As a metric predicting solubility, we calculated infinite dilution activity coefficients (ln­(γ)) for 28 lignin pentamers in 50 organic solvents using COSMO-RS, which have been shown to predict experimental trends in lignin solubility. ,− ,,, We then parameterized a regression model to predict ln­(γ) values as a function of five parameters: three parameters describing the solvent and two parameters describing the S- and H- contents of the lignin. We used Kamlet–Taft ( K – T ) parameters to identify solvents based on their proticity (α), basicity (β), and polarity (π).…”

“…Several studies have used empirical parameters, such as Hansen solubility parameters, − to guide solvent selection for fractionation, but these parameters do not capture variations in lignin composition. Recent computational studies using conductor-like screening model for realistic solvents (COSMO-RS) calculations or molecular dynamics (MD) simulations have also explored the molecular basis of lignin solubility but generally for a small range of lignin structures/solvents due to their computational expense. − There, thus, remains a need for methods to efficiently guide solvent selection for lignin solubilization while accounting for the heterogeneous population of possible lignin structures.…”

“…We first calculated infinite dilution activity coefficients (γ) for a wide range of lignin/solvent combinations by using COSMO-RS. Prior studies have shown that ln­(γ) predicted by COSMO-RS can serve as a quantitative metric that captures trends in lignin solubility. ,− ,,, However, COSMO-RS calculations alone are computationally expensive when applied to larger molecules, like lignin oligomers, inhibiting the exhaustive exploration of possible lignin compositions. We therefore used the COSMO-RS data to train a regression model that predicts ln­(γ) values based on simple descriptors of the solvent and lignin composition.…”

Characterization and molecular simulation of lignin in Cyrene pretreatment of switchgrass

“…[46][47][48][49] Recent work by Mohan et al provided an account of lignin-Cyrene and lignin-Cyrene : water interactions using a combination of COSMO-RS and all-atom molecular dynamics simulations and suggested that Cyrene has a preferential interaction with lignin when in mixtures with water and caused isolated lignin chains to adopt randomcoil like conformation. 50 However, the prior work made use of non-optimized force-field for Cyrene obtained from CGenFF, modelled a generic lignin, did not consider inter-lignin chain interactions, i.e. the behaviour of lignin aggregates, and performed MD simulations of only two of the experimental ratios considered here.…”